1. Technical Field
The present invention relates to a fuel pellet comprised primarily of cellulosic materials and densified thermoplastic materials. More particularly, the present invention relates to a method of manufacturing a fuel pellet so as to produce a clean and efficient industrial fuel with a high heat output.
2. Discussion of Related Art
Fuel pellets having different compositions of materials have been used for heating since the mid-nineteen eighties. Typically, the fuel pellets are burned in a stoker furnace, and are associated with residential style heating systems.
Due to increased restrictions in landfill requirements by the U.S. Environmental Protection Agency (EPA) and the diminishing quantities of naturally occurring fuels, there is a demand for new sources of energy. In addition, there has been a dramatic increase in cost for establishing new landfills which comply with U.S. Environmental Protection Agency requirements, for paper mill by-products. Recently, the EPA has enforced the requirement of double lining landfills for disposal of paper mill sludge. By converting paper mill sludge into fuel pellets, we not only create an alternative fuel source by recycling a waste product, but we eliminate the expense of double lining landfills. Beginning in 1984 with the first pellet-burning stove by Pyro Industries, there has been an increased interest in creating a pellet fuel comprised of wood based products, agricultural residues, waste paper and dried sludge.
In some foreign countries, such as Sweden, there has been a recent trend toward banning the burning of fossil based fuels for energy. Accordingly, such countries are currently seeking an alternative fuel source without dramatically compromising their energy requirements. By creating new forms of fuel which burn non-recyclable as well as recyclable waste materials, we preserve the environment, recycle otherwise non-disposable waste products, as well as maintain the world's limited quantity of natural fuel sources.
Several fuel pellets comprised of cellulosic materials have been patented. For example, U.S. Pat. No. 4,236,897 to Johnston discloses a fuel pellet comprised of natural cellulosic material and synthetic polymeric thermoplastic material. The cellulosic material being substantially 5 Mesh, having a moisture content of about 5 to about 15 percent by weight, and comprising from about 90 to 99 percent by weight of the fuel pellet. The thermoplastic material is disclosed as being between 5 and 10 Mesh and comprising about 1 to 10 percent by weight of the fuel pellet. Johnston further discloses seven samples of pellets having slightly different compositions, but all within the ranges disclosed. Each of the seven sample fuel pellets were burned in a stoker furnace having three spreader stokers and a vibrating grate. An average fuel analysis of the fuel pellets tested produced 9,160 BTU per pound, and at no time did it exceed 9,180 BTU per pound. Johnston further discloses using binding agents in the composition of the fuel pellet in addition to thermoplastic materials, such as paraffin slack wax and carnauba wax. Such additives are not desirable in our novel fuel pellet, as wax can not properly burn in a pulver furnace. Furthermore, both paraffin wax and carnauba wax would jeopardize the integrity of our novel fuel pellet.
U.S. Pat. No. 5,342,418 to Jesse discloses a method of making a fuel pellet comprised of cellulosic material. The fuel pellet described therein is comprised of 60 to 90 percent by weight of cellulosic material, and 10 to 40 percent by weight of a thermoplastic resin. The heat output of the fuel pellets is between 9,500 and 11,500 BTU per pound. Again, the fuel pellets disclosed in this patent is for use in a conventional stoker furnace and not a pulver furnace. The fuel pellet disclosed by Jesse purposefully produces an ash output of at least 1 percent by weight, so as to protect the equipment which carries the fuel into the furnace. Furthermore, ash is a necessary component for burning particles in a stoker furnace. Ash deposits are not a necessary component of our novel fuel pellet, which is designed for a pulver furnace, and therefore does not require ash deposits to maintain the burning cycle.
Other examples of patented fuel pellets and methods of making fuel pellets include: U.S. Pat. No. 5,141,526 to Chu disclosing a process for making fuel from waste sludge containing water, solids and oil; U.S. Pat. No. 4,810,255 to Fay, III et al. disclosing a method of manufacturing a fuel comprised of wood chips and wax; U.S. Pat. No. 4,529,407 to Johnston et al. disclosing a fuel pellet comprised of 97 to about 99 percent by weight of cellulosic material and about 1 to 3 percent by weight of thermoplastic material.
While each of the above described fuel pellet compositions and methods of making the fuel pellets function adequately, they each have drawbacks. The major drawback is that the fuel pellets described in the above cited references are not designed to burn in a pulver furnace. Each of the above described fuel pellets is designed to burn in a stoker furnace, and is therefore most desirable for a residential style furnace. Furthermore, the Chu fuel pellet and the Fay, III et al. fuel pellet each disclose the use of oil and wax particles, as well as thermoplastic films as part of the composition of the fuel pellet. The use of oil and wax based particles are not present in our novel fuel pellet. An important characteristic of our novel fuel pellet is that it burns in expansion, and that each of the particles within the pellet burn separately. The novel fuel pellet only functions properly if it's particles are bound together prior to burning, but break into their individual particles in the boiler. By mixing oil into the composition, we would jeopardize the ability of the pellet to maintain its shape. Additionally, wax is not capable of burning in a pulver style furnace. By mixing wax into the composition, we not only jeopardize the integrity of the pellet, but are left with the remains of the wax after the burning process, which must then be disposed.
Fuel pellets and other substances which are burned in a pulver furnace burn in expansion. As the pellet is placed in the pulver boiler, the pellet expands and breaks into the original particles which comprise the fuel pellet. Therefore, it is a requirement that all of the substances of the fuel pellet composition be capable of burning in a pulver furnace. For example, thermoplastic films are not capable of burning properly in a pulver furnace. Therefore, what is desirable is a fuel pellet comprised of cellulosic materials, densified thermoplastic materials, coal and other cellulosic based waste materials for burning in a pulver or stoker style furnace and producing a heating output of up to 16,000 BTU per pound.